第十七章 标准库特殊设施

17.1

	tuple<int, int, int> t{1, 2, 3};
	tuple<int, int, int> t1(1, 2, 3);

　　

17.2

	tuple<string, vector<string>, pair<string, int>> t;

　　

17.4

typedef tuple<vector<Sales_data>::size_type, vector<Sales_data>::const_iterator, vector<Sales_data>::const_iterator> tup;
vector<tup> findBook(const vector<vector<Sales_data>> &files, const string &book)
{
	vector<tup> vec;
	for (auto it = files.cebegin(); it != files.cend(); ++it) {
		auto found = equal_range(it->cbegin(), it->cend(), book, compareIsbn);
		if (found.first != found.second)
			vec.push_back(make_tuple(it - files.cbegin(), found.first, found.second));
	}
	return vec;
}

　　

17.5

typedef pair<vector<Sales_data>::size_type, pair<vector<Sales_data>::const_iterator, vector<Sales_data>::const_iterator>> Pair;
vector<Pair> findbook_pair(const vector<vector<Sales_data>> &files, const string &book) 
{  
    vector<Pair> ret;  
    for (auto it = files.cbegin(); it != files.cend(); ++it)  
    {  
        auto found = equal_range(it->cbegin(), it->cend(), book, compareIsbn);  
        if (found.first != found.second)  
            ret.push_back(make_pair(it - files.cbegin(), make_pair(found.first, found.second)));  
    }  
    return ret;  
} 

　　

17.6

struct matches_struct 
{  
    vector<Sales_data>::size_type st;  
    vector<Sales_data>::const_iterator first;  
    vector<Sales_data>::const_iterator second;  
    matches_struct(vector<Sales_data>::size_type s, vector<Sales_data>::const_iterator fi, vector<Sales_data>::const_iterator se): st(s), first(fi), second(se) {}  
};  

vector<matches_struct> findbook_struct(const vector<vector<Sales_data>> &f, const string &book)  
{  
    vector<matches_struct> ret;  
    for (auto it = f.cbegin(); it != f.cend(); ++it)  
    {  
        auto found = equal_range(it->cbegin(), it->cend(), book, compareIsbn);  
        if (found.first != found.second)  
            ret.push_back(matches_struct(it - f.cbegin(), found.first, found.second));  
    }  
    return ret;  
}

　　

17.7

倾向于书中的版本，更简洁、灵活

 

17.8

创建的是使用Sales_data默认构造函数创建的对象

这样的结果就是书名为空，其他数据为0

 

17.9

(a)：后六位为100000，前面58位全为0

(b)：后七位为1010101，前面25位全为0

(c)：若bstr包含的字符数多于8位，bv只包含bstr的前八位；否则，bv的前几位将被置零。当然，若出现非0/1的字符，会抛出异常

 

17.10

	bitset<22> b;
	int a[] = {1, 2, 3, 5, 8, 13, 21};
	for (auto &i : a)
		b.set(i);
	cout << b << endl;

　　

17.11

template <unsigned N>
class test {
public:
	test() = default;
	test(unsigned long long &u): b(u) { }
	test(string &s): b(s) { }
private:
	bitset<N> b;
};

int main()
{
	test<10> t1;
	test<10> t2;
}

　　

17.12

	void set_pos(size_t pos, bool bl = true)	//问题编号，真假解答的值 
	{
		b.set(pos, bl);
	}

　　

17.13

#include <iostream>
#include <string>
#include <bitset>
 
using namespace std;

template <unsigned N>
class test {
public:
	test() = default;
	test(unsigned long long &u): b(u) { }
	test(string &s): b(s) { }
	void set_pos(size_t pos, bool bl = true)	//问题编号，真假解答的值 
	{
		b.set(pos, bl);
	}
	int get_score(bitset<N> &b1)
	{
		auto bb = b ^ b1;
		bb.flip();
		return bb.count();
	}
private:
	bitset<N> b;
};

bitset<10> set_ans()
{
	string s;
	cout << "请输入标准答案："; 
	cin >> s;
	bitset<10> ans(s);
	return ans;
}

int main()  
{  
	bitset<10> ans = set_ans();			//正确答案 
	test<10> t;
	int cnt = 0, pos;
	cout << "请输入你认为正确的位置：";
	while (cin >> pos && cnt++ <= 10) {	
		t.set_pos(pos);
	}
	cout << "正确的答题数为：" << t.get_score(ans) << endl;
	return 0;  
}  

　　

17.14

#include <iostream>
#include <string>
#include <regex>
 
using namespace std;

int main()
{
	try {
		regex r("[[:alnum:]+", regex::icase);
	} catch (regex_error e) {
		cout << e.what() << "\ncode: " << e.code() << endl;
	}
	return 0;
}

　　

17.15

#include <iostream>
#include <string>
#include <regex>
 
using namespace std;

int main()
{
	regex r("[[:alpha:]]*[^c]ei[[:alpha:]]*", regex::icase);  
    string s;  
    cout << "Please input a word(enter 'q' to quit!): " << endl;  
    while(cin >> s && s != "q")  
    {  
        if(std::regex_match(s, r))  
            cout << s << " is okay!" << endl;  
        else  
            cout << s << " is not okay!" <<endl;  
  
        cout << "Please input a word(enter 'q' to quit!): " << endl;  
    }  
	return 0;
}

　　

17.16

只有一个单词为三个字符时才匹配

 

17.28

vector<unsigned> func()
{
	vector<unsigned> vec;
	static default_random_engine e;
    static uniform_int_distribution<unsigned> u;
	for (auto i = 0; i != 10; ++i)
		vec.push_back(u(e)); 
	return vec;
}

　　

17.29

vector<unsigned> func(unsigned seed)
{
	vector<unsigned> vec;
	static default_random_engine e(seed);
    static uniform_int_distribution<unsigned> u;
	for (auto i = 0; i != 10; ++i)
		vec.push_back(u(e)); 
	return vec;
}

　　

17.30

vector<unsigned> func(unsigned seed, unsigned mmin, unsigned mmax)
{
	vector<unsigned> vec;
	static default_random_engine e(seed);
    static uniform_int_distribution<unsigned> u(mmin, mmax);
	for (auto i = 0; i != 10; ++i)
		vec.push_back(u(e)); 
	return vec;
}

　　

17.31

每次循环中，分布返回的总是同一个值

 

17.32

到右大括号时，resp对象将被释放

 

17.33

#include <iostream>
#include <string>
#include <random>
 
using namespace std;

string trans1(const string &s1, const string &s2)
{
	string s = s1 + s2;
	return s;
}

string trans2(const string &s1, const string &s2)
{
	string s = s1;
	return s;
} 

int main()
{
	default_random_engine e;
	bernoulli_distribution b;
	bool bl = b(e);
	string ss;
	if (bl)	ss = trans1("love", "kzw");
	else	ss = trans2("love", "kzw");
	cout << ss << endl;
	return 0;
}

　　

17.34

#include <iostream>
#include <string>
#include <iomanip>
 
using namespace std;

int main()
{
	int i = 20;
	double d = 10, d1 = 30.1415926;
	bool bl = true, bp = false;
	cout << boolalpha << bl << " " << bp << " " << noboolalpha << bl << endl;
	cout << showbase << 20 << " " << oct << 20 << " " << hex << 20 << endl << dec << noshowbase;
	cout << setbase(8) << 20 << " " << 20 << endl;
	cout << showpoint << d << noshowpoint << endl;
	cout << showpos << i << noshowpos << endl;
	cout << d1 << " " << scientific << d1 << " " << fixed << d1 << " " << d1 << endl;
	cout << setw(10) << d1 << " " << setprecision(7) << d1 << endl;
	return 0;
}

　　

17.35

	cout << uppercase << hexfloat << sqrt(2.0) << endl;
	cout << nouppercase << defaultfloat;

　　

17.36

	double d0 = 3.14, d1 = 31.415, d2 = 520.1314, d3 = 11.11223344;
	cout << "d0: " << setw(12) << d0 << " next col" << endl
		 << "d1: " << setw(12) << d1 << " next col" << endl
		 << "d2: " << setw(12) << d2 << " next col" << endl
		 << "d3: " << setw(12) << d3 << " next col" << endl;

　　

17.37

当未遇到分隔符时，若已读取的字符数超过了size - 1时（下面的程序就是9），就会结束循环

但若遇到分隔符时，前面读取的字符数还未超过size - 1时，会打印该行（如空行），然后开始读取开始下一行（读取的字符数会清0）

小结：要想读取完整，那么字符数组和size都要设置的足够大，大到每一次读取可以遇到分隔符。

#include <iostream>
#include <fstream>
#include <string>
#include <iomanip>
#include <cmath>
 
using namespace std;

int main()
{
	ifstream in("data.txt");
	char str[100];
	do{
		in.getline(str, 10, '\n');
		cout << str << endl;
	} while(in);
	return 0;
}

　　

17.38

#include <iostream>
#include <fstream>
#include <string>
#include <iomanip>
#include <cmath>
 
using namespace std;

int main()
{
	ifstream in("data.txt");
	char str[100];
	do{
		//谨记上一题的教训，size应设置得足够大，至少大于最长的单词的长度 
		in.getline(str, 30, ' ');		//单词应该以空格分隔 
		cout << str << endl;
	} while(in);
	return 0;
}

　　

17.39

#include <iostream>
#include <fstream>
#include <string>
#include <iomanip>
#include <cstdlib>
#include <cmath>
 
using namespace std;

int main()
{
	fstream ios("data.txt", fstream::ate | fstream::in | fstream::out);
	if (!ios) {
		cerr << "Unable to open file!" << endl;
		return EXIT_FAILURE;
	}
	auto endMark = ios.tellg();
	ios.seekg(0, fstream::beg);
	string line;
	size_t cnt = 0;
	while (ios && ios.tellg() != endMark && getline(ios, line)) {
		cnt += line.size() + 1;
		auto mark = ios.tellg();
//		ifstream::pos_type mark = ios.tellg();
		ios.seekp(0, fstream::end);
		ios << cnt;
		if (mark != endMark)	ios << " ";
		ios.seekg(mark);
	}
	ios.seekp(0, fstream::end);
	ios << endl;
	return 0;
}